Coordinate XYZ limitation of 10,000 - Workaround questions
The limitation is on size of objects, not actual vertex location.
And according to this answer, there's no way around it.
The limit is actually ±10 000, so the maximum size of objects is 20 000 BU.


Workaround  


Move your origin point.
Since the zero point for this limitation is object's origin point, you can make a mountain 20 000 m high, by moving the origin point higher.




Funny sidenote:
It's actually 10 000 Blender units (which correspond to meters), so for Imperial units, the limit is 32808.4 ft.